Because you believe in the imaginary achievement called Double Career Slam, right? Except it would not change the basis of the comparison. Player B would be more accomplished (considerably so) at 3 of the 4 events. Why choose A, unless one is governed by the value system that sacrifices logic on the altar of obsession?
When you put it like "Double Career Slam" it sounds imaginary. Rather I see it as "more balanced Slam resume". Which is real merit. I'm a Rafa fan. I know lot of Roger fans who believes Rafa wont be greater than him if Rafa gets to 18 by winning solely RGs though Rafa has completed the Career Slam. I believe it's true. Now their reasoning can be interpreted in 3 ways:
1. Rafa should have "more balanced" title wins across all 4 Slams. ie, the standard deviation should be minimal. Something like 3 AO, 5 RG, 3 WC, 4 UO
2. Rafa should lead in title wins in 2 or 3 of the 4 Slams. ie, the median should be higher. Something like OP presented his case where Sampras leads Nadal in 3/4 Slams.
3. Rafa should have at least X title wins in each of the 4 Slams where X being higher is better.
- 1. penalizes for someone being too good at something. It's anti-specialization. It says like you not only have to win more from every Slam but you can not also be too good at something. I find it stupid. By that logic player A with 1-1-1-1 record is better than 1-1-1-7. Wrong according to me.
- 2. disregards whether the player has completed the Career Slam or not at all. In this case it supports Sampras being better than Nadal in Slams which I cant agree with. Rafa is simply one better than Sampras if all the Slams have equal weightage. Moot point here because I'm already talking from a point where uniformity matters.
- I dont see a weakness in .3. For this reason imo, Agassi > Sampras, accomplishment wise.
Hence my pick is 3. I also think 2. is a good indicator
if Career Slam is completed. I don't know which weighs higher, would love to see discussion on it, but I'm tempted to pick 3.